A patent foramen ovale (PFO) as shown in FIG. 1, is a persistent, one-way, usually flap-like opening in the wall between the right atrium 10 and left atrium 12 of the heart. Since left atrial (LA) pressure is normally higher than right atrial (RA) pressure, the flap typically stays closed. Under certain conditions, however, RA pressure can exceed LA pressure creating the possibility for right to left shunting that can allow blood clots to enter the systemic circulation. In utero, the foramen ovale serves as a physiologic conduit for right-to-left shunting. After birth, with the establishment of pulmonary circulation, the increased left atrial blood flow and pressure results in functional closure of the foramen ovale. This functional closure is subsequently followed by anatomical closure of the two over-lapping layers of tissue: septum primum 14 and septum secundum 16. However, a PFO has been shown to persist in a number of adults.
The cause of ischemic stroke remains cryptogenic (of unknown origin) in approximately 40% of cases. Especially in young patients, paradoxical embolism via a PFO is considered in the diagnosis. While there is currently no proof for a cause-effect relationship, many studies have confirmed a strong association between the presence of a PFO and the risk for paradoxical embolism or stroke. In addition, there is good evidence that patients with PFO and paradoxical embolism are at increased risk for future, recurrent cerebrovascular events.
The presence of a PFO has no therapeutic consequence in otherwise healthy adults. In contrast, patients suffering a stroke or transient ischemic attack (TIA) in the presence of a PFO and without another cause of ischemic stroke are considered for prophylactic medical therapy to reduce the risk of a recurrent embolic event. These patients are commonly treated with oral anticoagulants, which have the potential for adverse side effects, such as hemorrhaging, hematoma, and interactions with a variety of other drugs.
In certain cases, such as when anticoagulation is contraindicated, surgery may be used to close the PFO. To suture a PFO closed requires attachment of septum secundum to septum primum with either an interrupted or a continuous stitch, which is the common way a surgeon shuts the PFO under direct visualization.
Nonsurgical closure of PFOs has become possible with the advent of umbrella devices and a variety of other similar mechanical closure designs, developed initially for percutaneous closure of atrial septal defects (ASD). These devices allow patients to avoid the potential side effects often associated with anticoagulation therapies.
Currently available designs of septal closure devices, however, present such drawbacks as technical complexity of implantation procedure, high complication rates (thrombus, fractures, conduction system disturbances, perforations, residual leaks), high septal profile, large masses of foreign material, and lack of anatomic conformability especially to the PFO flap-like anatomy, as most were originally designed to close ASD's, which are true holes. Additionally, some septal closure devices are complex to manufacture, which can result in lack of consistency in product performance.